The present invention relates to a method and apparatus for forming rod-shaped articles of the tobacco processing industry, and more particularly to improvements in a method and apparatus for forming a continuous filler which is thereupon wrapped and subdivided into rod-shaped articles of selected length.
It is well known to make a continuous cigarette rod by admitting particles of tobacco into an elongated path which is defined by a foraminous conveyor and wherein the thus formed stream is held and caused to advance with the conveyor by suction. The surplus of tobacco particles is removed by a trimming device and the trimmed stream (filler) is thereupon draped into a web of cigarette paper or other suitable material and is subdivided by a cutoff to yield plain cigarettes, cigars or cigarillos of desired length. It is also known to monitor the density of the filler (either prior or subsequent to draping) and to regulate the position of the trimming device with reference to the conveyor (i.e., the rate of removal of tobacco particles from the stream) in dependency on fluctuations of the monitored density so as to ensure that the density of the filler will match or closely approximate a predetermined value. Such mode of making rod-shaped articles of the tobacco processing industry can be resorted to for the mass production of tobacco-containing products as well as for the making of certain types of filter rod sections which are thereupon united with tobacco-containing articles to form therewith filter cigarettes, cigars or cigarillos.
U.S. Pat. No. 3,132,650 discloses a cigarette rod making machine wherein the surplus which is removed by the trimming device from an unequalized tobacco stream is not returned into the distributor of the machine but is immediately admitted to the unequalized stream ahead of the trimming device. A drawback of such proposal is that the machine will produce an unsatisfactory filler if the deviation of the quantity of tobacco in the untrimmed stream from an average value will persist for a longer interval of time. Thus, the tobacco stream which approaches the trimming station will contain an excessive amount of surplus tobacco if the trimming operation involves removal of larger-than-average quantities of surplus tobacco. On the other hand, if the quantity of surplus tobacco in the untrimmed stream is below average, the filler is likely to contain less tobacco than necessary for the making of acceptable rod-shaped articles. In order to overcome such problems, the patented apparatus further comprises means for monitoring the position of the trimming plane and of utilizing the thus obtained signals for adjustment of the distributor in a sense to ensure that the surplus in the steam which is formed on the foraminous conveyor approximates or matches a preselected value, i.e., in a sense to reduce or eliminate fluctuations of surplus tobacco in the untrimmed tobacco stream.
U.S. Pat. No. 4,190,061 discloses a cigarette rod making machine wherein the surplus, which is removed by the trimming device, is monitored and the resulting signals are used to regulate the rate of tobacco feed to the stream building zone with a view to ensure that the quantity of surplus tobacco will remain at least substantially constant. The monitoring of the surplus involves generating a signal which is indicative of the difference between the height of the untrimmed stream and the distance of the trimming plane from the foraminous conveyor for the tobacco stream. The distance between the trimming plane and the conveyor is ascertained by monitoring the distance between the trimming device and the conveyor.
It has been found that such prior proposals fail to ensure the formation of a highly satisfactory filler stream, especially as concerns its density and the quantity of circulated surplus tobacco.